DIAGNOSIS This is typically a bandwidth issue. Your home network might be congested, or the camera's signal is weak where it's installed.
FIX First, test your own connection. On your phone, try switching from cellular data to your home Wi-Fi, or vice versa. If it works on one but not the other, the problem is with that network. If you're on home Wi-Fi, check the camera's signal strength in the Tapo app under Device Settings > Wi-Fi Signal. If it's fair or poor, that's your issue. Try moving the camera closer to the router, or consider a Wi-Fi extender.
IF THAT DIDN'T WORK The stream quality might be too high for your upload speed. In the Tapo app, go to the camera's settings and look for Video Quality or Streaming Resolution. Try switching from "HD" or "Full HD" down to "SD" or "Balanced" and see if the live feed becomes stable.
HEADS UP Watching the live feed remotely uses your home's internet upload speed, which is often much slower than download. If someone else at home is video calling, gaming, or uploading large files, it can easily choke the camera's stream.